1. Field of the Invention
The present invention relates to an apparatus configured to determine a cylinder deactivation state for an internal combustion engine having a mechanism that is configured to perform cylinder deactivation control to deactivate a part of plural cylinders.
2. Description of the Related Art
There has been an internal combustion engine including a cylinder deactivation mechanism that deactivates operation of a part of plural cylinders. In such an internal combustion engine, it is possible to switch between all cylinder operation for operating all of the plural cylinders and cylinder deactivation operation for deactivating a part of cylinders in accordance with operational conditions.
Japanese Patent Application Laid-open (JP-A) No. 6-146937 discloses a method for detecting failure of the switching between the all cylinder operation and the cylinder deactivation operation. According to this method, the switching failure is detected by comparing intake manifold pressure at the all cylinder operation estimated based on detected engine revolution speed and throttle valve opening with intake manifold pressure actually detected by a sensor arranged at an intake manifold.
Further, JP-A No. 2005-139962 discloses the following method. That is, a detected intake air amount and a set value based on revolution speed of an internal combustion engine are compared after an instruction to start cylinder deactivation control is outputted to the internal combustion engine during deceleration operation of a vehicle. Then, failure occurrence in the cylinder deactivation control is determined when the detected intake air amount is equal to or larger than a threshold value. This method utilizes generation of large difference between the intake air amounts at the all cylinder operation and at the cylinder deactivation operation during deceleration.
Furthermore, JP-A No. 2003-83148 discloses a method to determine apparatus failure by monitoring oil pressure with an oil pressure detection sensor which is provided at a downstream side of an oil passage switching device to switch between activation and deactivation of an intake valve and an exhaust valve of a cylinder in an engine which deactivates a part of cylinders during deceleration.
The failure determination method of a cylinder deactivation mechanism in the related art determines failure of the cylinder deactivation mechanism as a whole, so that identification of an activated cylinder and a deactivated cylinder is not done. In order to monitor whether or not the cylinder deactivation mechanism is appropriately operated in accordance with instructions from an electronic control unit, it is desired to determine which cylinder is activated or deactivated.
Therefore, a method for determining a cylinder deactivation state has been needed for an engine having a cylinder deactivation mechanism.